An internal rotor type motor in which an annular stator is fixed to the inside of a case and a rotor is rotated inside the stator is known. The stator is configured by winding coils around a plurality of slots of a stator core, and the rotor having a permanent magnet is rotated by a rotating magnetic field generated by applying, for example, a three phase current to the coil.
When current flows through the coils of the stator, the coils and the stator core generate heat and thus the temperature of the stator core increases. For this, there is an electric rotating machine configured so that a cooling passage is provided inside the case without depending only on natural heat radiation to external air, and a cooling fluid is caused to flow through the cooling passage to transfer the heat of the stator core to the cooling fluid via the case, thereby actively suppressing temperature increase of the stator.
In the case having the cooling passage therein as described above, in order to increase the rigidity of the case, columnar supports that connect the inner wall and the outer wall of the case are distributed and arranged in the cooling passage. In addition, in order to prevent the surface vibration of the outer wall of the case, ribs are provided on the outer surface of the outer wall of the case (for example, refer to Patent Document 1).